A mobile phone (also known as a wireless phone, cell phone, or cellular phone) is a communication device used for mobile voice or data communication over a cellular network of specialized base stations known as cell tower stations or cell towers. In addition to the standard voice function of a mobile phone, current mobile phones may support many additional services. One of these popular services is global positioning system (GPS) assistance.
A conventional method of obtaining accurate GPS assistance includes using a mobile phone to identify its current cell and to pass that data to a network server. The network server accesses a database that correlates a carrier cell's identification information to a geographic location. By then referencing a real-time GPS satellite database, a computer program may immediately discern which satellites are most visible to that mobile phone's cell. The orbits for these satellites, which are complied into a file called an ephemeris, are located and transmitted to the mobile phone. The mobile phone can then easily lock to the satellite network, as described in more detail below.
FIG. 1 illustrates a conventional satellite communication system used for a satellite GPS application. In the figure, satellite 104, satellite 106 and satellite 108 are in orbits around Earth 102 in orbit 110, orbit 112 and orbit 114, respectively. The distance from any specific location on Earth 102 to each of satellite 104, satellite 106 and satellite 108 varies with time.
FIG. 2 illustrates a satellite PGS application used in a conventional communication system. In the figure, a user 202, is operating a mobile phone 204, within range of a cell tower 206. Further, satellites 104 and 106 are orbiting above Earth 102. Mobile phone 204 is operable to communicate with cell tower 206, as indicated by dashed communication line 208, and to communicate with satellite 104, as indicated by dotted communication line 210.
A cellular network connects cell phones to one another via cell towers and satellites. Each cell tower communicates with one or more satellites, for example, cell tower 206 communicates with satellites 104 and 106 as indicated by dotted communication lines 212 and 214, respectively. The satellites additionally are able to communicate with one another, for example, satellite 104 and 106 communicate with each other as indicated by dotted communication line 216. Orbiting around Earth, each satellite is able to communicate to the cellular network by communicating with a plurality of cell towers.
FIG. 3 geographically illustrates a conventional cellular network. In the figure, region 302 is populated by multiple cells, a portion of which are illustrated as cells 304 through 348 (evenly numbered). Each cell is served by a fixed transmitter from one or more cell towers. A mobile phone user, within a cell, communicates via a cell tower geographically located within that cell For example, with additional reference to FIG. 2, if user 202 were located at point 350, which is within cell 328, then user 202 would communicate with others via cell tower 206 within cell 328.
Referring back to FIG. 2, when user 202 wants to obtain GPS assistance, via mobile phone 204, mobile phone 204 needs to communicate with a satellite within a GPS network. However, as discussed above, a plurality of satellites 104, 106 and 108 are constantly orbiting about Earth. As such, it may be difficult for mobile phone 204 to locate and lock onto a particular satellite.
A conventional method of addressing the problem of locating and locking onto a particular satellite, includes using the cellular network. Specifically, mobile phone 204 is used to communicate with cell tower 206. Cell tower 206 recognizes its current cell identification information, for example the identification information of cell 328 in FIG. 3. Conventional databases list geographical location of cell towers, which includes cell tower 206. Further, some conventional GPS service providers correlate the geographical location of cell towers to the plurality of GPS satellites through an ephemeris database.
Cell tower 206 is able to contact any one of many cell phone service providers having information that corresponds to the geographical location of cell tower 206. The cell phone service provider may then references GPS service provider to obtain a real-time GPS satellite ephemeris that determines the closest orbiting satellite to cell tower 206. As mobile phone 204 is within the transmission area of cell tower 206, then the closest orbiting satellite to cell tower 206 is likely the closest orbiting satellite to mobile phone 204.
Once the closest orbiting satellite to mobile phone 204 is identified, the GPS service provider provides communication data to the cell phone service provider, which then provides the communication data to mobile phone 204 via cell tower 206 to enable mobile phone 204 to locate and lock onto the satellite. In the example illustrated in FIG. 2, satellite 104 is closer than satellite 106 to cell tower 206. This enables mobile phone 204 to communicate with satellite 104 as indicated by dotted communication line 210.
The conventional approach of accessing a GPS service discussed above is not easy to implement because the region covered by each cell tower is limited. In addition, cell phone providers are required to pay royalties to utilize this technique.
What is needed is a system and method to lock to a GPS satellite without using the location data of a cell tower within a cellular communication system.